<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>09_计算器练习</title>
</head>
<body>
    <input type="text" placeholder="请输入数字1" id="i1"> <br>
    <input type="text" placeholder="请输入数字2" id="i2"> <br>
    <button onclick="calc('+')">加</button>
    <button onclick="calc('-')">减</button>
    <button onclick="calc('*')">乘</button>
    <button onclick="calc('/')">除</button>
    <h4>运算结果:<span></span></h4>
    <script>
        function calc(o) {
            //获取用户输入的两个数字
            let n1 = document.querySelector("#i1").value;
            let n2 = document.querySelector("#i2").value;
            //修改获取到的值,默认为string类型,要改为number类型
            n1 = parseFloat(n1);
            n2 = parseFloat(n2);
            //获取用来显示结果的span元素
            let spanE = document.querySelector("span");
            //根据不同的运算符执行不同的运算结果
            switch (o){
                case '+':
                    //将运算结果放置到span中进行显示
                    spanE.innerHTML = n1 + n2;
                    break;
                case '-':
                    spanE.innerHTML = n1 - n2;
                    break;
                case '*':
                    spanE.innerHTML = n1 * n2;
                    break;
                case '/':
                    if(n2!=0){
                        spanE.innerHTML = n1 / n2;
                    }else{
                        alert("除数不能为0!");
                    }
            }
        }
    </script>
</body>
</html>